The present invention relates to liquid crystal displays, and more particularly, to liquid crystal displays having mechanisms that collect ambient light to illuminate the display.
A liquid crystal display (LCD) includes pairs of opposing transparent electrodes, and liquid crystal, which is contained between the electrodes. The liquid crystal is electro-optically anisotropic. The application of a predetermined voltage between the electrodes forms an electric field with the liquid crystal. This causes the liquid crystal to exhibit optical properties that correspond to the field density. The LCD has a plurality of pixels. An image is formed by applying a different voltage to each pixel so that the pixel obtains the desirable brightness. A typical LCD employs a backlight to illuminate the display from behind.
In addition to a compact and thin profile, an LCD has low power consumption. Thus, LCDs are often used in office automation equipment and audio visual equipment. Portable equipment having LCDs are often used outdoors, where ambient light is abundant. In such cases, the ambient light may be used in lieu of the backlight to further decrease power consumption by a significant amount.
A prior art LCD will now be described with reference to FIG. 1, which is a cross-sectional view showing an LCD 100.
The LCD 100 has a display panel 10, a backlight 80 arranged behind the display panel 10, and a case 70 housing the display panel 10 and the backlight 80. The backlight 80 includes a light guide plate 20, a light source 50 arranged on one end of the light guide plate 20, a collecting lens 60 arranged on the other end of the light guide plate 20, a diffusing portion 30 arranged on a front side of the light guide plate 20, and a reflecting portion 40 arranged below or on the rear side of the light guide plate 20.
The light source 50, which may be a fluorescent lamp, is encompassed by a reflector 51. The light guide plate 20 may be made of acrylic resin. A convex lens, which is formed separately from the light guide plate 20 or integrally with the light guide plate 20, may be employed as the collecting lens 60. The case 70 has an opening 71, which is located at a position corresponding to the collecting lens 60 which allows the collecting lens 60 to project outward through the opening 71 to allow the collecting lens 60 to collect light from outside of the case 70.
Light, which is emitted by the light source 50 or collected by the collecting lens 60, is transmitted to the light guide plate 20. The light is then refracted by the light guide plate 20 toward the diffusing plate 30 or the reflecting portion 40. The reflecting portion 40 may be a plate, a film or a coating including a reflecting surface. The diffusing portion 30 may also be a plate, a film or a coating including a diffusing surface. The reflecting portion 40 reflects the light toward the diffusing portion 30 through the light guide plate 20. The diffusing portion 40 diffuses the light so that some of the light forms an even light plane that is irradiated toward the display panel 10, while the remaining light is returned toward the light guide plate 20 to be reflected again by the reflecting portion 40. Accordingly, the intensity of the light attenuates as it bounces back and forth horizontally between the diffusing portion 30 and the reflecting portion 40.
The display panel 10 does not emit light by itself. Thus, the display panel 10 is illuminated from behind. The light permeability of the display panel 10 is controlled in order to distribute the light passing through the display panel 10 in a desired pattern so that images can be visualized on the display panel 10.
The light source 50 is lit to illuminate a bright image on the display panel 10 when ambient light is insufficient, such as during indoor usage. The light source 50 is turned off when ambient light is abundant, such as during outdoor usage on a sunny day. Under such conditions, the light collected by the collecting lens 60 is used to illuminate the display panel 10. Thus, although power for driving the display panel 10 is still necessary, power for driving the light source 50 becomes unnecessary. This reduces the total power consumption of the LCD 100.
The relationship between brightness relative to positions on the display panel 10 during sole usage of the collecting lens 60, is shown in the graph of FIG. 2. The horizontal axis represents the lateral position on the display panel 10, while the vertical axis represents the brightness. Position A indicates the illuminated right end on the display panel 10 that is closest to the collecting lens 60 and position B indicates the illuminated left end of the display panel 10. The light collected by the collecting lens 60 travels from position A to position B, as viewed in the graph of FIG. 2. As shown in the graph, there are several brightness peaks. The value of the peak closest to position A is maximum, and the values of the other peaks decrease as the distance from position A increases.
The distance between adjacent peaks is determined by the size of the illuminated portion on the display panel 10. For example, in a two inch LCD, the width of which is 45 millimeters, the distance between adjacent peaks is approximately 15 millimeters. In a fifteen inch LCD, the width of which is 190 millimeters, the distance between adjacent peaks is approximately 60 millimeters. Such peaks, or brightness fluctuation, results in the illumination of visual brightness stripes and lowers the quality of the En image illuminated on the display panel 10.
Accordingly, it is an objective of the present invention to provide an LCD having uniform brightness.
To achieve the above objective, the present invention it provides a liquid crystal display comprising a liquid crystal display panel, a light guide plate arranged adjacent to the display panel, a light transmitter optically connected to the light guide plate, and a light collector optically connected to the light transmitter.
Other aspects and advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.